Protected switch and techniques to manufacture the same

ABSTRACT

Briefly, micromechanical system (MEMS) switches that utilize protective layers to protect electrical contact points.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/897,667, filed on Jul. 22, 2004, which is a divisional of U.S. patentapplication Ser. No. 10/738,200,filed on Dec. 16, 2003.

FIELD

The subject matter disclosed herein generally relates to micromechanicalsystem (MEMS) switches.

DESCRIPTION OF RELATED ART

The use of MEMS switches has been found to be advantageous overtraditional solid-state switches. For example, MEMS switches have beenfound to have superior power efficiency, low insertion loss, andexcellent electrical isolation. However, a switch is often required toperform billions of switching cycles. Over time, the metal contacts maywear down thereby increasing contact resistance and leading toreliability issues.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts in cross section a switch in accordance with anembodiment of the present invention.

FIG. 2 depicts one possible process that may be used to construct aswitch in accordance with an embodiment of the present invention.

FIGS. 3A to 3K depict cross sections of structures constructed inaccordance with an embodiment of the present invention.

FIG. 4 depicts a process that can be used to provide a protection layer.

FIG. 5 depicts one possible process that may be used to construct aswitch in accordance with an embodiment of the present invention.

FIGS. 6A to 6I depict cross sections of structures constructed inaccordance with an embodiment of the present invention.

Note that use of the same reference numbers in different figuresindicates the same or like elements.

DETAILED DESCRIPTION

Structure

FIG. 1 depicts in cross section a switch 100, in accordance with anembodiment of the present invention. Switch 100 may include base 310,arm 335, contact surface 343, second contact 320C, and actuation 320B.Base 310 may support actuation 320B, second contact 320C and arm 335.When a voltage is applied between actuation 320B and arm 335, arm 335may lower contact surface 343 to electrically contact second contact320C. In accordance with an embodiment of the present invention, secondcontact 320C may have a durable protective coating layer 340 that mayprotect second contact 320C from wear. Protective coating layer 340 mayinclude an array of densely packed multi-walled or single-walled carbonprotections and may be formed over second contact 320C. When the voltagebetween actuation 320B and arm 335 is removed, arm 335 may restore toits original shape.

An array of carbon nanotubes may conduct a very high density of currentwith low resistance. Carbon nanotubes may also provide mechanicalproperties of high flexibility, strength, and resilience. Carbonnanotubes may provide electrical conductivity even when elasticallydeformed. Each nanotube may have a very small diameter (e.g., 1 to 100nm). An array of nanotubes may provide electrical contact with non-flatsurfaces by a large number of contact points. Furthermore, nanotubes maypenetrate any contamination layer on the contact surface thus increasingthe reliability of electrical conductivity with the contact.

Process to Make Structure

In accordance with an embodiment of the present invention, FIG. 2depicts one possible process that may be used to construct switches.Action 210 may include providing metal layer 320 over silicon surface310. FIG. 3A depicts in cross section an example structure that mayresult from action 210. A suitable implementation of silicon surface 310is a silicon wafer. Suitable materials of layer 320 include silver,gold, and/or aluminum. A suitable technique to provide metal layer 320includes sputter deposition or physical vapor deposition.

Action 220 may include removing portions of metal layer 320 to formlayers 320A, 320B, and 320C. FIG. 3B depicts in cross section an examplestructure that may result from action 220. Layer 320B may be referred toas actuation 320B. Layer 320C may be referred to as second contact 320C.In action 220, a suitable technique to remove portions of layer 320includes: (1) applying photolithography using a mask and photoresist tocover the portions of the exposed surface of layer 320 that are not tobe removed; (2) using fluorinated hydrocarbons (e.g., CF₄ or C₂F₆), or acombination of nitric acid with sulfuric acid to remove portions oflayer 320 that are not covered by photoresist; and (3) removingphotoresist by using a resist stripper solvent.

Action 230 may include providing and shaping a catalyst layer. FIG. 3Cdepicts in cross section an example structure that may result fromaction 230. Catalyst layer 325 may increase adhesion of a protectivelayer as well increase mechanical strength and also reduce contactresistance of the protective layer. Suitable materials of the catalystlayer include: cobalt, iron, nickel, molybdenum or any metal. A suitabletechnique to provide the catalyst layer includes sputtering,evaporation, or any method to deposit thin metal film. A suitabletechnique to remove portions of the catalyst layer to form catalystlayer 325 includes: (1) applying photolithography using a mask andphotoresist to cover the portions of the exposed surface of the catalystlayer that are not to be removed; (2) using fluorinated hydrocarbons(e.g., CF₄ or C₂F₆), or a combination of nitric acid with sulfuric acidto remove portions of the catalyst layer that are not covered byphotoresist; and (3) removing photoresist by using a resist strippersolvent. A suitable thickness of catalyst layer 325 may be 1 to 100 nm(from contact with second contact 320C).

Action 240 may include providing and shaping a sacrificial layer. FIG.3D depicts in cross section an example structure that may result fromaction 240. Suitable materials of a sacrificial layer include SiO₂,polymer, glass-based materials, and/or metals (e.g., copper). Suitabletechniques to provide the sacrificial layer include (1) sputtering,chemical vapor deposition (CVD), spin coating, or physical vapordeposition followed by (2) polishing a surface of the sacrificial layerusing, e.g., chemical mechanical polish (CMP). Suitable techniques toshape the sacrificial layer to form sacrificial layer 330 include: (1)applying photolithography using a mask and photoresist to cover theportions of the exposed surface of the sacrificial layer that are not tobe removed; (2) providing an HF solution to remove exposed portions ofthe sacrificial layer; and (3) removing photoresist by using a resiststripper solvent.

Action 250 may include providing and shaping a beam. FIG. 3E depicts incross section an example structure that may result from action 250. Asuitable material of the beam includes gold and/or aluminum. The beammay be the same material but does not have to be the same material asthat of second contact 320C. A suitable technique to provide the beamincludes sputter deposition or physical vapor deposition. A suitabletechnique to remove portions of the beam to form beam 335 includes: (1)applying photolithography using a mask and photoresist to cover theexposed surface of the beam that are not to be removed; (2) usingfluorinated hydrocarbons (e.g., CF₄ or C₂F₆) or a combination of nitricacid with sulfuric acid; and (3) removing photoresist by using a resiststripper solvent.

Action 260 may include removing sacrificial layer 330. FIG. 3F depictsin cross section an example structure that may result from action 260. Asuitable technique to remove remaining sacrificial layer 330 includessubmerging the structure depicted in FIG. 3E into an HF solution.

Action 270 may include providing protection layer 340 over catalystlayer 325. FIG. 3G depicts in cross section an example structure thatmay result from action 270. In one implementation, protection layer 340includes an array of adjacent and potentially contacting carbonnanotubes. For example, FIG. 3H depicts an array of adjacent carbonnanotubes 341 bonded to catalyst layer 325, although an array ofadjacent carbon nanotubes 341 may be bonded to other surfaces. Eachnanotube may have a very small diameter (e.g., 1 to 100 nm). Action 270may include utilizing a CVD chamber to provide methane, ethylene, orcarbon monoxide gas and heating the chamber to form carbon over thecatalyst layer 325. A thickness of protection layer 340 may be based ontime that gas flows over the catalyst layer 325. In one implementation,catalyst layer 325 may prevent reaction of the second contact 320C withreactive gases and improve the efficiency of metal catalysts that areapplied during growth of protection layer 340.

In one embodiment of process 200, a catalyst layer 325 is not providedand instead, action 270 includes providing protection layer 342 overlayer 320C (hereafter action 270A). Protection layer 342 includes anarray of adjacent and potentially contacting carbon nanotubes. FIG. 31depicts in cross section an example structure that may result fromaction 270A. In this embodiment, a bonding material such as thiol can beused to bond protection layer 342 to layer 320C. The bonding materialmay provide electrical signal conductance between the protection layer342 and layer 320C.

FIG. 4 depicts a process that can be used in action 270A to provideprotection layer 342 over second contact 320C. In action 410, carbonnanotubes may be covered with a protective film such as photoresist overportions that are not to be bonded with second contact 320C. In action420, an adhesive such as thiol may be bonded to the portion of thecarbon nanotubes that are to be bonded to second contact 320C. In action430, carbon nanotubes with adhesive portions may be dispersed into asolvent. In action 440, carbon nanotubes may be bonded to second contact320C by for example providing the solvent mixture with carbon nanotubesover second contact 320C. For example, a tip or side of each carbonnanotube may be bonded to second contact 320C.

Some embodiments of process 200 may include action 280. Action 280 mayinclude coating or partially coating protection layer 340 or 342 withrespective second metal layer 345 or 355. For example, action 280 mayinclude utilizing physical deposition or sputtering methods to providesecond metal layer 345 or 355. Suitable materials of second metal layer345 and 355 include, but are not limited to, titanium, gold, aluminum,and/or silver. For example FIGS. 3J and 3K depict examples of switcheswith respective second metal layer 345 and 355 provided over respectiveprotection layers 340 and 342. Second metal layers 345 and 355 canreduce contact resistance between respective protection layers 340 and342 and an opposite electrode (e.g., surface 343). Second metal layer345 or 355 may reduce Van de Waals interaction when second metal layer345 or 355 is in contact with the opposite electrode, so that twoelectrodes can be separate more easily when the switch is turned “off”to provide a faster switching action.

Second Structure

FIG. 6F depicts in cross section a switch 700, in accordance with anembodiment of the present invention. Switch 700 may include base 610,arm 650, second contact 620C, and actuation 620B. Base 610 may supportactuation 620B, second contact 620C, and arm 650. When a voltage isapplied between actuation 620B and arm 650, arm 650 may lower toelectrically contact second contact 620C using surface 675. Inaccordance with an embodiment of the present invention, arm 650 may havea durable protective coating layer 660 that may protect arm 650 fromwear. When the voltage between actuation 620B and arm 650 is removed,arm 650 may restore to its original shape. Protective coating layer 660may include an array of densely packed multi-walled or single-walledcarbon protections.

An array of carbon nanotubes may conduct a very high density of currentwith low resistance. Carbon nanotubes may also provide mechanicalproperties of high flexibility, strength, and resilience. Carbonnanotubes may provide electrical conductivity even when elasticallydeformed. Each nanotube may have a very small diameter (e.g., 1 to 100nm). An array of nanotubes may provide electrical contact with non-flatsurfaces by a large number of contact points. Furthermore, nanotubes maypenetrate any contamination layer on the contact surface thus increasingthe reliability of electrical conductivity with the contact.

Process to Make Structure

In accordance with an embodiment of the present invention, FIG. 5depicts one possible process that may be used to construct switches.Action 510 includes providing and shaping a metal layer over a siliconsurface. FIG. 6A depicts in cross section an example structure that mayresult from action 510. A suitable implementation of silicon surface 610is a silicon wafer. Suitable materials of layer 620 include silver,gold, and/or aluminum. A suitable technique to provide metal layer 620includes sputter deposition or physical vapor deposition. Shaping themetal layer 620 may also include removing portions of layer 620 to formlayers 620A, 620B and 620C. A suitable technique to remove portions oflayer 620 includes: (1) applying photolithography using a mask andphotoresist to cover the exposed surface of layer 620 that are not to beremoved; (2) applying fluorinated hydrocarbons (e.g., CF₄ or C₂F₆), or acombination of nitric acid with sulfuric acid; and (3) removingphotoresist by using a resist stripper solvent. Herein, layer 620B mayotherwise be referred to as actuation 620B whereas layer 620C mayotherwise be referred to as second contact 620C.

Action 520 includes providing and shaping a sacrificial layer. FIG. 6Bdepicts in cross section an example structure that may result fromaction 520. Suitable materials of the sacrificial layer include SiO₂,polymer, glass-based materials, and/or metals (e.g., copper). Suitabletechniques to provide the sacrificial layer include (1) sputtering,chemical vapor deposition (CVD), or physical vapor deposition followedby (2) polishing a surface of the sacrificial layer using, e.g.,chemical mechanical polishing (CMP). Regions to form a portion of an armand a catalyst region may be removed from the sacrificial layer.Suitable techniques to shape the sacrificial layer includes: (1)applying photolithography using a mask and photoresist to cover theexposed surface of the sacrificial layer that is not to be removed; (2)providing an HF solution to remove exposed portions of the sacrificiallayer; and (3) removing photoresist by using a resist stripper solvent.The depth of removal of sacrificial layer can be controlled by the HFetching speed and etching time.

Action 530 includes forming a catalyst layer in a portion of thesacrificial layer. FIG. 6C depicts in cross section an example structurethat may result from action 530. Catalyst layer 640 may increaseadhesion of a protective layer formed over the catalyst layer as well asincrease mechanical strength and reduce contact resistance of theprotective layer. Suitable materials of catalyst layer 640 includecobalt, iron, nickel, molybdenum or any metal. A suitable technique toprovide catalyst layer 640 includes sputtering, evaporation, or anymethod to deposit thin metal film over the relevant portion of thesacrificial layer. A suitable thickness of catalyst layer 640 may be 1to 100 nm (from contact with arm 650). A suitable technique to removeportions of the catalyst layer to form catalyst layer 640 includes: (1)applying photolithography using a mask and photoresist to cover theportions of the exposed surface of the catalyst layer that are not to beremoved; (2) using fluorinated hydrocarbons (e.g., CF₄ or C₂F₆), or acombination of nitric acid with sulfuric acid to remove portions of thecatalyst layer that are not covered by photoresist; and (3) removingphotoresist by using a resist stripper solvent. Another suitabletechnique to remove portions of the catalyst layer to form catalystlayer 640 includes polishing a surface of catalyst layer 640 andsacrificial layer using, e.g., chemical mechanical polishing (CMP).

Action 540 may include providing and shaping a beam. FIG. 6D depicts incross section an example structure that may result from action 540. Asuitable material of the beam includes gold and/or aluminum. The beammay be the same material but does not have to be the same material asthat of metal layer 620. A suitable technique to provide the beamincludes sputter deposition or physical vapor deposition. A suitabletechnique to shape the beam includes: (1) applying photolithographyusing a mask and photoresist to cover the exposed surface of the beamthat are not to be removed; (2) using fluorinated hydrocarbons (e.g.,CF₄ or C₂F₆), or a combination of nitric acid with sulfuric acid; and(3) removing photoresist by using a resist stripper solvent.

Action 550 may include removing sacrificial layer 630. A suitabletechnique to remove sacrificial layer 630 includes submerging thestructure depicted in FIG. 6D into an HF solution.

Action 560 may include providing protection layer 660 over catalystlayer 640. FIG. 6F depicts in cross section an example structure thatmay result from action 560. In one implementation, protection layer 660includes an array of adjacent and potentially contacting carbonnanotubes. For example, the array of carbon nanotubes may be similar tothose described with respect to FIG. 3H. Each nanotube may have a verysmall diameter (e.g., 1 to 100 nm). Action 560 may include utilizing aCVD chamber to provide methane, ethylene, or carbon monoxide gas andheating the chamber to form carbon over catalyst layer 640. A thicknessof protection layer 660 may be based on time that gas flows over thecatalyst layer 640. In one implementation, catalyst layer 640 mayprevent reaction of arm 650 with reactive gases and improve theefficiency of metal catalysts that are applied during growth ofprotection layer 660.

In one embodiment of process 500, catalyst layer 640 is not provided andinstead, action 560 includes providing protection layer 645 onto arm 650(hereafter action 560A) and opposite second contact 620C. FIG. 6Gdepicts in cross section an example structure that may result fromaction 560A. In this embodiment, a bonding material such as thiol can beused to bond protection layer 645 to arm 650. The bonding material mayprovide electrical signal conductance between protection layer 645 andarm 650. A process similar to that described with respect to FIG. 4 maybe used to provide protection layer 645 over arm 650.

Some embodiments of process 500 may include action 570. Action 570 mayinclude coating or partially coating protection layer 645 or 660 withrespective second metal layer 670 or 680. For example, action 570 mayinclude utilizing simple physical deposition or sputtering methods toprovide second metal layer 670 or 680. Suitable materials of secondmetal layer 670 and 680 include, but are not limited to, titanium,aluminum, gold, and/or silver. For example FIGS. 6H and 6I depictexamples of switches with second metal layers 670 and 680 provided overrespective protection layers 645 and 660. Second metal layers 670 and680 can reduce contact resistance between protection layers 645 and 660and an opposite electrode (e.g., second contact 620C). Second metallayers 670 and 680 may reduce Van de Waals interaction with an oppositeelectrode, so that two electrodes can be separate more easily when theswitch is turned “off” to provide a faster switching action.

Modifications

The drawings and the forgoing description gave examples of the presentinvention. The scope of the present invention, however, is by no meanslimited by these specific examples. Numerous variations, whetherexplicitly given in the specification or not, such as differences instructure, dimension, and use of material, are possible. The scope ofthe invention is at least as broad as given by the following claims.

1. An apparatus comprising: a base layer; a contact portion formed onthe base layer; a protective layer formed over a portion of the contactportion, wherein the protective layer comprises carbon nanotubes; and anarm structure formed on the base layer.
 2. The apparatus of claim 1,further comprising an actuation formed on the base layer.
 3. Theapparatus of claim 2, wherein the actuation comprises a conductivemetal.
 4. The apparatus of claim 1, wherein the base layer comprises asilicon structure.
 5. The apparatus of claim 1, wherein the contactportion comprises a conductive metal.
 6. The apparatus of claim 1,wherein the arm structure comprises a conductive metal.
 7. The apparatusof claim 1, further comprising a conductive layer provided over aportion of the protective layer.
 8. The apparatus of claim 1, furthercomprising an intermediate layer formed between the protective layer andthe contact portion.
 9. The apparatus of claim 8, wherein theintermediate layer comprises a catalyst layer.
 10. The apparatus ofclaim 8, further comprising a conductive layer provided over a portionof the protective layer.
 11. An apparatus comprising: a base layer; acontact portion formed on the base layer; a protective layer formed overa portion of the contact portion, wherein the protective layer comprisescarbon nanotubes; an actuation formed on the base layer; and an armstructure formed on the base layer.
 12. The apparatus of claim 11,wherein the base layer comprises a silicon structure.
 13. The apparatusof claim 11, wherein the contact portion comprises a conductive metal.14. The apparatus of claim 11, wherein the actuation comprises aconductive metal.
 15. The apparatus of claim 11, wherein the armstructure comprises a conductive metal.
 16. The apparatus of claim 11,further comprising a conductive layer provided over a portion of theprotective layer.
 17. The apparatus of claim 11, further comprising anintermediate layer formed between the protective layer and the contactportion.
 18. The apparatus of claim 17, wherein the intermediate layercomprises a catalyst layer.
 19. The apparatus of claim 17, furthercomprising a conductive layer provided over a portion of the protectivelayer.
 20. The apparatus of claim 11, wherein each of the carbonnanotubes has a diameter in a range of approximately 1 nm to 100 nm. 21.The apparatus of claim 11, further comprising a thiol adhesive to bondcarbon nanotubes to the portion of the contact portion.
 22. Theapparatus of claim 11, wherein tips of nanotubes are bonded to theportion of the contact portion.
 23. The apparatus of claim 11, whereinthe protective layer comprises an array of closely spaced nanotubes. 24.An apparatus comprising: a base layer; a contact portion formed on thebase layer; an intermediate layer formed over a portion of the contactportion; a protective layer formed over a portion of the intermediatelayer, wherein the protective layer comprises carbon nanotubes; anactuation formed on the base layer; and an arm structure formed on thebase layer.
 25. The apparatus of claim 24, further comprising aconductive layer provided over a portion of the protective layer. 26.The apparatus of claim 24, wherein the base layer comprises a siliconstructure.
 27. The apparatus of claim 24, wherein the contact portioncomprises a conductive metal.
 28. The apparatus of claim 24, wherein theintermediate layer comprises a catalyst layer.
 29. The apparatus ofclaim 24, wherein the protective layer comprises an array of closelyspaced nanotubes.
 30. The apparatus of claim 24, wherein the actuationcomprises a conductive metal.
 31. The apparatus of claim 24, wherein thearm structure comprises a conductive metal.
 32. The apparatus of claim24, wherein tips of nanotubes are bonded to the portion of theintermediate layer.
 33. The apparatus of claim 24 wherein each of thecarbon nanotubes has a diameter in a range of approximately 1 nm to 100nm.